These are the two guys who never failed a drug test and dominated their divisions for many years. I think it's only fair to compare these two to determine the #1 GOAT. If I made a mistake in one of my comparisons feel free to correct me, it's late at night here.
When you look at the stats and the facts objectively, I think there's no real option but to acknowledge GSP as the #1 GOAT.
TITLES WON
Fedor - PRIDE Heavyweight Championship, WAMMA Heavyweight Championship, RINGS Openweight Championship
GSP - UFC Welterweight Championship (x2), UFC Middleweight Championship, UCC Welterweight Championship
TITLE DEFENCES
Fedor - 3 (Nogueira, Crocop, Mark Hunt)
GSP - 9 (Fitch, BJ Penn, Alves, Dan Hardy, Koscheck, Shields, Ondit, Nick Diaz, Johny Hendricks)
TIME AS CHAMPION
Fedor - 1663 days (Won the title 03/16/2003, Pride folds 10/04/2007)
GSP - 2064 days (Won the title 04/19/2008, vacated 12/13/2013), + 140 days of first title run
UFC CHAMPIONS BEATEN
Fedor - 5 (Coleman, Randleman, Sylvia, Arlovski, Mir), 1 interim champ (Nogueira)
GSP - 6 (Hughes, Sherk, BJ Penn, Matt Serra, Johny Hendricks, Michael Bisping), 1 interim champ (Condit)
UFC HALL OF FAMERS BEATEN
Fedor - 2 (Mark Coleman, Nogueira)
GSP - 3 (Matt Hughes, Matt Serra, BJ Penn)
LOSSES
Fedor - 5 (4 KO/TKO, 1 SUB), 1 avenged (Kosaka)
GSP - 2 (1 KO/TKO, 1 SUB), both losses avenged (Hughes x2, Serra)
FIGHTMETRIC STATS
*Note: FightMetric doesn't seem to have Fedor's last 4 fights logged in, which included the KO loss to Mitrione and war with Maldonado, so his stats may appear slightly better than what they actually are.
Fedor:
Significant Strikes landed per minute: 3.18
Significant Striking Accuracy: 51%
Significant Strike Defence: 63%
Takedown Accuracy: 63%
Takedown Defence: 82%
GSP:
Significant Strikes landed per minute: 3.78
Significant Striking Accuracy: 53%
Significant Strike Defence: 72%
Takedown Accuracy: 74%
Takedown Defence: 83%
So it seems like GSP has outdone Fedor in pretty much every way.